Method of manufacturing software controlled antenna

ABSTRACT

An antenna is fabricated by: passing first dielectric strip through metallization station and forming a plurality of radiating patches on top surface of the first dielectric strip and a plurality of delay lines on bottom surface of the first dielectric strip; passing a second dielectric strip through metallization station and forming a common ground on top surface of the second dielectric strip and a plurality of feed lines on bottom surface of the second dielectric strip; passing the first and second dielectric strips through an alignment material deposition station and depositing an alignment layer; depositing spacers; depositing liquid crystal material over the top surface of the second dielectric strip or over the bottom surface of the first dielectric strip; adhering the first and second dielectric strips together to form a multi-layer strip; cutting the multi-layer strip into individual antennas.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/667,584, filed on Aug. 2, 2017, and claims priority benefitfrom U.S. Provisional Application No. 62/382,489, filed on Sep. 1, 2016,U.S. Provisional Application No. 62/382,506, filed on Sep. 1, 2016, andU.S. Provisional Application No. 62/431,393, filed on Dec. 7, 2016, andis also related to U.S. patent application Ser. No. 15/421,388, filed onJan. 31, 2017, and U.S. patent application Ser. No. 15/654,643, filed onJul. 19, 2017, the disclosures of all of which are incorporated hereinby reference in their entireties.

BACKGROUND 1. Field

This disclosure relates to method of manufacturing antennas having anarray of radiating elements forming a directionally controlled radiationbeam. The parameters of radiation of the radiating elements can becontrolled by software.

2. Related Art

Much of today's communication is done wirelessly, or at least part ofthe path is wireless. All wireless communication requires antennas onboth transmit and receive sides. Generally, much of the transmission maybe done utilizing an omni-directional antenna. In such antennas, thetransmission power drops in reverse relation to the distance cubed.Thus, in order to reach many users the transmission power is usuallyrelatively high as compared to directional antennas. Also, when severalomni-directional antennas operate simultaneously, e.g., multiple devicesin an Internet café, the various transmissions may interfere with eachother, or at least reduce the quality of transmission and reception inthat environment. Signal to Noise ratio plus interference are criticalmeasures in any modern wireless network.

Another trend is for mobile devices to be fabricated out of block ofmetal, e.g., aluminum, such that much of the body of the device mayblock RF radiation. Consequently placement of the antenna is veryrestricted. Moreover, since mobile devices normally use several wirelesscommunication protocols, they may require several antennas, eachdesigned for the frequency of the specific protocol, e.g., WiFi,Bluetooth, NFC, etc. Since the real estate area on mobile devices is ata high premium, it is very difficult to design and place such antennaswithin the device.

In a prior disclosure, the subject inventor has disclosed an antennathat utilizes variable dielectric constant to control thecharacteristics of the antenna. Details about that antenna can be foundin U.S. Pat. No. 7,466,269, the entire disclosure of which isincorporated herein by reference. This disclosure builds on the basicelements disclosed in the '269 patent and provides methods forfabricating a software controlled antenna with further improvements andfeatures.

SUMMARY

The following summary is included in order to provide a basicunderstanding of some aspects and features of the invention. Thissummary is not an extensive overview of the invention and as such it isnot intended to particularly identify key or critical elements of theinvention or to delineate the scope of the invention. Its sole purposeis to present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented below.

Disclosed is a software controlled antenna and a method for fabricatinga software controlled antenna. According to some embodiments, an antennaarray is printed or deposited over a sandwich of layers that includesvariable dielectric-constant material. The value of the variabledielectric-constant material at various points over the antenna iscontrolled via software, hence changing the operational characteristicsof the antenna using software. The disclosed method provides processesfor fabricating the various elements of the antenna and the sandwich oflayers forming the antenna. This is one embodiment of practicallyimplementing the variable dielectric true time delay phase shiftmechanism into a full antenna system, other options such as waveguidefeeds into the variable dielectric section are also feasible and can beimplemented in a similar way.

The sandwich of layers may be a standard flat panel display or amultilayer dielectric substrates, wherein images depicted on the flatpanel display are software controlled with a program designed to changethe dielectric constant, thus providing scanning and tuning ability tothe array. That is, different images are programmed according tospecifically desired change in the dielectric property of differentpixels under different patches or feed-lines of the array, therebycontrolling the frequency and/or directivity of the array, and thedirection of the radiation beam of the antenna (i.e., enablingelectronic steering of the antenna).

When the antenna is not visible to a user, e.g., when the antenna isinside a WiFi HotSpot, the array can be made using metallic conductor,such as copper, aluminum, etc. Conversely, when the antenna is visibleand visibility of the flat panel display is important, e.g., in mobiledevices, the array can be made using transparent conductor, such as ITO,AZO etc. Of course, transparent conductor can also be used fornon-visible antenna and metallic conductor can be used with visibleantennas.

An aspect addressed by disclosed embodiment is the RF feeding to theradiating element. Since the radiating patches and the delay lines areprovided over a variable dielectric constant material which can changethe value of its dielectric constant during operation, coupling the RFsignal to the patch and delay line needs to be done in a way that is“shielded” from the changes in the dielectric constant.

According to disclosed aspects, a method for fabricating a multilayeredantenna is provided, comprising the non-ordered steps of: fabricating atop substrate by forming radiating elements on a top surface of a firstinsulating plate, and forming a plurality of corresponding delay lineson a bottom surface of the insulating plate; fabricating a bottomsubstrate by forming a common ground electrode on a top surface of asecond insulating plate, the common ground electrode having a pluralityof apertures, and forming a plurality of conductive feed lines on abottom surface of the second insulating plate; forming an alignmentlayer over: the top surface of the bottom substrate, over the bottomsurface of the top substrate, or on the top surface of the bottomsubstrate and over the bottom surface of the top substrate; providinginsulating spacers over the alignment layer; attaching a sealer over theperiphery of the top surface of the bottom substrate or the bottomsurface of the top substrate; flowing liquid crystal among theinsulating spacers; and, attaching the bottom substrate to the topsubstrate.

According to disclosed embodiments, having the patch directly above athin insulating layer that is directly above the variable dielectricconstant enables using the variable dielectric to change the centerfrequency of the antenna.

According to other aspects, a method of manufacturing antennas isprovided, comprising the non-ordered steps of: providing a first rollerof first dielectric strip; providing a second roller of a seconddielectric strip; passing the first dielectric strip throughmetallization station and forming a plurality of radiating patches ontop surface of the first dielectric strip and a plurality of delay lineson bottom surface of the first dielectric strip; passing the seconddielectric strip through metallization station and forming a commonground on top surface of the second dielectric strip and a plurality offeed lines on bottom surface of the second dielectric strip; passing thefirst and second dielectric strips through an alignment materialdeposition station and depositing an alignment layer over the topsurface of the second dielectric strip, over the bottom surface of thefirst dielectric strip, or on the top surface of the second dielectricstrip and over the bottom surface of the first dielectric strip;depositing spacers over the top surface of the second dielectric stripor over the bottom surface of the first dielectric strip; depositingliquid crystal material over the top surface of the second dielectricstrip or over the bottom surface of the first dielectric strip; adheringthe first and second dielectric strips together to form a multi-layerstrip; and, cutting the multi-layer strip into individual antennas.

According to yet further aspects, a method for fabricating an antenna isprovided, comprising the non-ordered steps of: obtaining a firstdielectric plate and forming on the first dielectric plate a pluralityof RF radiating elements and a plurality of feed lines, each feed linebeing configured to communicate RF radiation to one of the radiatingelements; obtaining a second dielectric plate and forming on the seconddielectric plate a common ground layer and forming in the common groundlayer a plurality of apertures, each aperture being configured to alignwith one of the delay lines; forming a plurality of RF feed lines on thesecond dielectric plate, so as to form a corporate feed; providing analignment material on: the first dielectric plate, the second dielectricplate, or on both the first and second dielectric plates; attaching thefirst and second dielectric plates to each other while providing spacersso as to define a void in between the first and second dielectricplates; and, injecting liquid crystal material into the void between thefirst and second dielectric plates.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, exemplify the embodiments of the presentinvention and, together with the description, serve to explain andillustrate principles of the invention. The drawings are intended toillustrate major features of the exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of actualembodiments nor relative dimensions of the depicted elements, and arenot drawn to scale.

FIG. 1 illustrates a cross-section of a software controlled antennaaccording to one embodiment.

FIG. 2 illustrates a top elevation view of a software controlled antennaaccording to one embodiment.

FIG. 3 illustrates a top elevation view of a software controlled antennaaccording to another embodiment.

FIG. 4 illustrates a top elevation view of a software controlled antennaaccording to another embodiment.

FIG. 5 illustrates a cross-section of a software controlled antennaaccording to yet another embodiment.

FIG. 6 illustrates a cross-section of one radiating element of asoftware controlled antenna according to yet another embodiment.

FIG. 7, illustrates a top “transparent” view of the embodiment of FIG.6.

FIG. 8 illustrates an omni-directional steerable antenna according toone embodiment.

FIG. 9 illustrates a method according to an embodiment utilizing any ofthe software defined antennas described herein.

FIG. 10 is a block diagram illustrating how the antenna of any of thedisclosed embodiments can be incorporated in a standard IEEE 802.11Naccess point.

FIG. 11 illustrates the flow of a process for fabricating an antennaaccording to one embodiment, while FIG. 11A illustrates a modifiedprocess.

FIG. 12 illustrates the flow of a process for fabricating an antennaaccording to another embodiment.

FIG. 13 illustrates the flow of a process for fabricating an antennaaccording to yet another embodiment.

FIG. 14 illustrates a roll-to-roll process for making antennas accordingto embodiments of the invention.

DETAILED DESCRIPTION

The detailed description starts with the description of the antenna, andthen proceeds to the description of the method for making the antenna.Embodiments of the inventive antenna will now be described withreference to the drawings. Different embodiments or their combinationsmay be used for different applications or to achieve different benefits.Depending on the outcome sought to be achieved, different featuresdisclosed herein may be utilized partially or to their fullest, alone orin combination with other features, balancing advantages withrequirements and constraints. Therefore, certain benefits will behighlighted with reference to different embodiments, but are not limitedto the disclosed embodiments. That is, the features disclosed herein arenot limited to the embodiment within which they are described, but maybe “mixed and matched” with other features and incorporated in otherembodiments.

As for the antenna itself, the following aspects are noted. According todisclosed embodiments, an antenna is provided comprising: an LCD screenhaving a common ground contact, a plurality of addressable pixelcontacts, and a top dielectric; an array of radiating elements providedover the top dielectric; conductive delay lines, each connected to oneof the radiating elements; and a transmission feed provided below theLCD screen and coupled to the delay lines. A controller is coupled tothe common contact and to each of the addressable pixel contacts, thecontroller being preprogrammed to energize selective ones of the pixelcontrol contacts to change the spatial directivity of the radiatingelements.

Disclosed embodiments also provide a multi-layer antenna, comprising: atop dielectric, a bottom dielectric, a variable dielectric constantmaterial sandwiched between the top dielectric and the bottomdielectric, a plurality of conductive electrodes defining pixels withinthe variable dielectric constant material, a common ground electrode, atleast one radiating patch provided over the top dielectric, eachradiating patch having a corresponding delay line coupled to theradiating patch, a feed line provided below the bottom dielectric, andan RF coupling between the feed line and the delay line. The couplingmay be a conductive line passing through corresponding windows formed inthe common ground electrode.

Embodiments of the invention provide a wireless access point,comprising: a transceiver; an antenna array comprising an LCD screenhaving a common contact, a plurality of pixel control contacts, and atop dielectric; an array of radiating elements provided on top of thetop dielectric; and plurality of delay lines, each connected to one ofthe radiating elements; a plurality of feed lines connected at one endto the transceiver and the opposite end one of the delay lines; and, acontroller coupled to the common contact and to each of the pixelcontrol contacts, the controller being preprogrammed to activateenergize selective ones of the pixel control contacts to change spatialdirectivity of the plurality of radiating elements.

A further aspect is a method for operating the antenna, comprising:scanning a radiation cone formed by radiating elements of the antenna;using transmissions received during the scanning, identifying specificlocations in space of each originating transmission; from theoriginating transmissions, identifying locations of unauthorizedtransmissions; controlling the antenna to present a null to directionsof the unauthorized transmissions; and performing directed communicationwith each authorized transmission by controlling the antenna to steerthe radiation cone towards the authorized directions. Scanning theradiation cone can be performed by applying voltages to change thedielectric constant presented under the delay lines of the antenna.Optionally, for each authorized transmission, identifying thetransmitting device and determining the device's network and accesspolicies, and applying the network and access policies to thecommunications from the identified device, thereby forming an “RFfirewall.”

FIG. 1 illustrates a cross-section of a software controlled antennaaccording to one embodiment. In FIG. 1 multi-layer antenna havingvariable dielectric-constant material is constructed by having variabledielectric constant (VDC) material, e.g., liquid crystals 105 sandwichedbetween a top dielectric 115 and a bottom dielectric 110. The liquidcrystals are controlled by applied voltage from voltage potential source130 to desired contacts 120, which define pixels of the multi-layerantenna. In that sense, the contacts 120 form addressable contactsenabling individual addressing of each contact by a processor. Theground potential of voltage potential source is coupled to the bottomcommon ground electrode 125. The antenna comprises an array of radiatingelements, e.g., patches 135 that are interconnected via delay lines 140.The patches 135 and the delay lines 140 are provided on the topdielectric 115.

In one example either or both dielectrics 110 and 115 is made of aRogers® (FR-4 printed circuit board) or PTFE based materials, and thedelay lines 140, radiating patches 135, and/or common ground electrode125, may be a conductor formed on the Rogers. Rather than using Rogers,a PTFE (Polytetrafluoroethylene or Teflon®), PET (Polyethyleneterephthalate), or other low loss material may be used.

It has been discovered by the inventor that improved results can beachieved if the RF feed can be provided from below the multi-layersantenna. In fact, it was discovered that superior results can beachieved if the RF feed is coupled from below the common ground bottomelectrode 125. As noted by the inventor, providing the feed line belowthe common ground helps isolate the RF feed from the delay lines and theDC or AC voltage applied to the VDC layer. FIG. 1 illustrates anembodiment of a feed that is provided from below the layers, and belowthe common ground electrode 125. As shown in FIG. 1, the ground side ofthe RF Tx/Rx (transceiver) 150 is coupled to the common ground electrode125. However, the signal side is connected to feed electrode 155, whichis provided on the bottom of dielectric 110. The coupling may be by,e.g., a coaxial cable 162 connected to coaxial connector 160. In thisembodiment, vias are formed in the entire sandwich structure, includingholes or windows in the common ground electrode 125, top and bottomdielectrics 115 and 110, and VDC layer 105, so that the feed electrode155 can be connected to the delay line 140. By using this arrangement,the signal of source 130 is insulated or decoupled from the RF signal ofTx/Rx 150, and the changes in dielectric constant of material 105 do notaffect the signal traveling in the feed electrode 155, but rather onlythe signal traveling in delay line 140 and radiating patch 135.

Using software, the value of the variable dielectric-constant materialin the areas just below the patches 135 can be changed by applyingvoltage to the relevant pixels, to thereby control the frequencymatching of the patches. Similarly, the voltage applied to the pixelsunder the delay lines 140 can be controlled to change the spatialdirectivity of the array, or the rotational polarity of the signal.Either action acts only on the signal traveling though the relevantpart, i.e., radiating patch 135 or delay line 140, but not on the signaltraveling on feed electrode 155. Those do not need to be pixels and canbe areas that are defined as we wish.

Thus, according to this embodiment, a multi-layer antenna is provided,comprising: a top dielectric, a bottom dielectric, a variable dielectricconstant material sandwiched between the top dielectric and the bottomdielectric, a plurality of conductive electrodes defining pixels withinthe variable dielectric constant material, a common ground electrode, atleast one radiating patch provided over the top dielectric, eachradiating patch having a corresponding delay line coupled to theradiating patch, a feed line provided below the bottom dielectric, andan RF coupling between the feed line and the delay line. The couplingmay be a conductive line passing through corresponding windows formed inthe common ground electrode 125.

This can be seen more clearly in FIG. 2, which is a top view of an arrayof 2×2 radiating elements 235 with delay lines 240 provided on the topdielectric 215. The cross section of the embodiment of FIG. 2 is similarto that of FIG. 1, except that a single via is provided in the locationmarked by circle 265, and a contact is made to the feed electrode thatis provided below the dielectric 210, which are not visible in thisview. In this embodiment the single contact via is chosen to be at thesymmetric geometrical center of the array and feed line. In theparticular example of FIG. 2, the via location provides 180° rotationalsymmetry; however, other rotational symmetries can be used, e.g., 30°,90°, etc.

When the via is provided at the geometrical center, the signalpropagates evenly through all of the array elements. The operationalcharacteristics of the antenna can then be controlled by applyingvoltage to various pixels to change the orientation of the liquidcrystals at the pixels location. For example, when the same voltage isapplied to the pixels residing directly under all of the patches 235,the resonant frequency of the patches 235 can be changed, therebychanging the operational frequency of the antenna. On the other hand, byapplying different potentials under the delay lines, the resultingradiation cone can be steered, thereby directing the antenna to aparticular location in space or scanning the antenna, without physicallymoving the antenna. That is, the change in dielectric constant under thedelay lines causes a delay in the propagation of signal in that delayline, thus causing a phase shift in the radiating signal.

Another feature is presented in FIG. 3, wherein the delay lines areformed as meandering conductive lines in order to enable wider range ofcontrol over the delay line, especially in tight real estate when thepatches are closely packed together. The antenna of FIG. 3 is somewhatsimilar to that of FIG. 2, except that each delay line 340 is formed asa meandering line, such that its length covers more pixels.Consequently, more pixels are available to control the dielectricconstant over the length of the delay line.

In the previous embodiments, all of the delay lines were connectedtogether and fed from a single feeding point. However, this is not arequirement. For example, in the embodiment of FIG. 4 each of themeandering delay lines has a corresponding feed point 465, which iscoupled to a feed line through a corresponding coupling. In such anarrangement the accumulation of the signals from the radiating patchesis done below the sandwich structure of the antenna by, e.g., havinginterconnection of all of the feeding lines. Thus, in this embodiment amulti-layer antenna is provided, comprising: a top dielectric, a bottomdielectric, a variable dielectric constant material sandwiched betweenthe top dielectric and the bottom dielectric, a plurality of conductiveelectrodes defining pixels within the variable dielectric constantmaterial, a common ground electrode, at least one radiating elementprovided over the top dielectric, each radiating element having: acorresponding delay line coupled to the radiating patch, a correspondingfeed line provided below the bottom dielectric, and corresponding a RFcoupling between the feed line and the delay line.

FIG. 5 is a cross-section of an antenna according to yet anotherembodiment. The embodiment of FIG. 5 is similar to that of FIG. 1,except that the radiating patches 535 and the delay lines 540 areprovided on different levels of the multi-layer structure of theantenna. Specifically, a cover insulating layer 517 is provided over thetop dielectric 515. The cover insulating layer 517 may be Glass, PET,Rogers, PTFE, etc. The delay lines 540 are provided between the topdielectric 515 and the cover insulating layer 517. The radiating patches535 are provided over the cover insulating layer 517. Holes are providedin the cover insulating layer 517, so that contacts 519 can electricallyconnect the delay lines 540 to their respective radiating patches 535.

FIG. 6 illustrates a cross section at a location of one radiatingelement according to another embodiment of the multi-layer antenna. Thisstructure can repeat for as many radiating elements as needed to form anarray. The structure and operation of the embodiment can be betterunderstood from the following description of FIG. 6, with furtherreference to FIG. 7, which is a top “transparent” view. FIG. 6illustrates a cross section of relevant sections of the antenna at thelocation of the radiating element 635. FIG. 7 provides a top“transparent” view that is applicable to all of the embodimentsdescribed herein, including the embodiment of FIG. 6. Thus, in studyingany of the embodiments disclosed herein, the reader should also refer toFIG. 7 for a better understanding.

A cover insulating layer 617 is generally in the form of a dielectric(insulating) plate or a dielectric sheet, and may be made of, e.g.,glass, PET, PTFE, Rogers, etc. The radiating patch 635 is formed overthe cover insulating layer 617 by, e.g., adhering a conductive film,sputtering, printing, etc. At each patch location, a via is formed inthe cover insulating layer 617 and is filled with conductive material,e.g., copper, to form contact 619, which connects physically andelectrically to radiating patch 635. A delay line 640 is formed on thebottom surface of cover insulating layer 617 (or on top surface of topdielectric 615, which functions as an upper binder), and is connectedphysically and electrically to contact 619. That is, there is acontinuous DC electrical connection from the delay line 640 to radiatingpatch 635, through contact 619. As shown in above embodiments, the delayline 640 may be a meandering conductive line and may take on any shapeso as to have sufficient length to generate the desired delay, therebycausing the desired phase shift in the RF signal.

The delay in the delay line 640 is controlled by the variable dielectricconstant (VDC) plate 602 having variable dielectric constant material605. While any manner for constructing the VDC plate 602 may be suitablefor use with the embodiments of the antenna, as a shorthand in thespecific embodiments the VDC plate 602 is shown consisting of upperbinder 615, (e.g., glass PET, etc.) variable dielectric constantmaterial 605 (e.g., twisted nematic liquid crystal layer), and bottombinder 610. In other embodiments one or both of the binder layers 615and 610 may be omitted. Alternatively, adhesive such as epoxy or glassbead spacers may be used instead of the binder layers 615 and/or 610.

In some embodiments, e.g., when using twisted nematic liquid crystallayer, the VDC plate 602 also includes an alignment layer that may bedeposited and/or glued onto the bottom of cover insulating layer 617, orbe formed on the upper binder 615. The alignment layer may be a thinlayer of material, such as polyimide-based PVA, that is being rubbed orcured with UV in order to align the molecules of the LC at the edges ofconfining substrates.

The effective dielectric constant of VDC plate 602 can be controlled byapplying DC potential across the VDC plate 602. For that purpose,electrodes are formed and are connected to controllable voltagepotential. There are various arrangements to form the electrodes, andone example is shown in the arrangement of FIG. 6, wherein twoelectrodes 620 and provided—one next to the other—wherein the twoelectrodes define a pixel. As one example, one of the electrodes 620 isshown connected to variable voltage potential 641, while the otherelectrode 620 is connected to ground. As one alternative, shown inbroken line, the other electrode 620 may also be connected to a variablepotential 649. Thus, by changing the output voltage of variablepotential 641 and/or variable potential 649, one can change thedielectric constant of the VDC material in the vicinity of theelectrodes 620, and thereby change the RF signal traveling over delayline 640. Changing the output voltage of variable potential 641 and/orvariable potential 649 can be done using a controller, Ctl, running asoftware that causes the controller to output the appropriate controlsignal to set the appropriate output voltage of variable potential 641and/or variable potential 649. Thus, the antenna's performance andcharacteristics can be controlled using software—hence softwarecontrolled antenna.

At this point it should be clarified that in the subject description theuse of the term ground refers to both the generally acceptable groundpotential, i.e., earth potential, and also to a common or referencepotential, which may be a set potential or a floating potential.Similarly, while in the drawings the symbol for ground is used, it isused as shorthand to signify either an earth or a common potential,interchangeably. Thus, whenever the term ground is used herein, the termcommon or reference potential, which may be set or floating potential,is included therein.

As with all RF antennas, reception and transmission are symmetrical,such that a description of one equally applies to the other. In thisdescription it may be easier to explain transmission, but receptionwould be the same, just in the opposite direction.

In transmission mode the RF signal is applied to the feed line 655 viaconnector 660 (e.g., a coaxial cable connector). As shown in FIG. 6, inthis embodiment there is no electrical DC connection between the feedline 655 and the delay line 640. However, in this disclosed embodimentthe layers are designed such that an RF short is provided between thefeed line 655 and delay line 640. As illustrated in FIG. 6, a commonground electrode 625 is formed on the top surface of back planeinsulator (or dielectric) 612 or the bottom surface of bottom binder610. The common ground electrode 625 is generally a layer of conductorcovering the entire area of the antenna array. At each RF feed locationa window (DC break) 623 is provided in the common ground electrode 625.The RF signal travels from the feed line 655, via the window 623, and iscapacitively coupled to the delay line 640. The reverse happens duringreception. Thus, a DC open and an RF short are formed between delay line640 and feed line 655.

In one example, the back plane insulator 612 is made of a Rogers® (FR-4printed circuit board) and the feed line 655 may be a conductive lineformed on the Rogers. Rather than using Rogers, a PTFE(Polytetrafluoroethylene or Teflon®) or other low loss material may beused.

To further understand the RF short (also referred to as virtual choke)design of the disclosed embodiments, reference is made to FIG. 7. Oneshould note that similar elements in the drawings have the samereferences, except in a different series, e.g., in FIG. 7 the 7xx seriesis used. Also, FIG. 7 illustrates an embodiment with two delay lines 740connected to a single radiating patch 735, such that each delay line maycarry a different signal, e.g., at different polarization. The followingexplanation is made with respect to one of the delay lines, as the othermay have similar construction.

In FIG. 7 the radiating patch 735 is electrically DC connected to thedelay line 740 by contact 719. So, in this embodiment the RF signal istransmitted from the delay line 740 to the radiating patch 735 directlyvia the contact 719. However, no DC connection is made between the feedline 755 and the delay line 740; rather, the RF signal is capacitivelycoupled between the feed line 755 and the delay line 740. This is donethrough an aperture in the common ground electrode 725. As shown in FIG.6, the VDC plate 602 is positioned below the delay line 640, but in FIG.7 it is not shown, so as to simplify the drawing for betterunderstanding of the RF short feature. The common ground electrode 725is partially represented by the hatch marks, also showing the window (DCbreak) 723. Thus, in the example of FIG. 7 the RF path is radiatingpatch 735, to contact 719, to delay line 740, capacitively throughwindow 723 to feed line 755.

For efficient coupling of the RF signal, the length of the window 723,indicated as “L”, should be set to about half the wavelength of the RFsignal traveling in the feed line 755, i.e., λ/2. The width of thewindow, indicated as “W”, should be set to about a tenth of thewavelength, i.e., λ/10. Additionally, for efficient coupling of the RFsignal, the feed line 755 extends about a quarter wave, λ/4, beyond theedge of the window 723, as indicated by D. Similarly, the terminus end(the end opposite contact 719) of delay line 740 extends a quarter wave,λ/4, beyond the edge of the window 723, as indicated by E. Note thatdistance D is shown longer than distance E, since the RF signaltraveling in feed line 755 has a longer wavelength than the signaltraveling in delay line 740.

To summarize the disclosure so far, according to disclosed embodiments,an antenna is provided comprising: an LCD screen having a common groundcontact, a plurality of addressable pixel contacts, and a topdielectric; an array of radiating elements provided over the topdielectric; conductive delay lines, each connected to one of theradiating elements; and a transmission feed provided below the LCDscreen and coupled to the delay lines. A controller is coupled to thecommon contact and to each of the addressable pixel contacts, thecontroller being preprogrammed to energize selective ones of the pixelcontrol contacts to change the spatial directivity of the radiatingelements.

Embodiments disclosed above also provide a multi-layer antenna,comprising: a top dielectric, a bottom dielectric, a variable dielectricconstant material sandwiched between the top dielectric and the bottomdielectric, a plurality of conductive electrodes defining pixels withinthe variable dielectric constant material, a common ground electrode, atleast one radiating patch provided over the top dielectric, eachradiating patch having a corresponding delay line coupled to theradiating patch, a feed line provided below the bottom dielectric, andan RF coupling between the feed line and the delay line. The couplingmay be a conductive line passing through corresponding windows formed inthe common ground electrode.

Embodiments of the invention provide a wireless access point,comprising: a transceiver; an antenna array comprising an LCD screenhaving a common contact, a plurality of pixel control contacts, and atop dielectric; an array of radiating elements provided on top of thetop dielectric; and plurality of delay lines, each connected to one ofthe radiating elements; a plurality of feed lines connected at one endto the transceiver and the opposite end one of the delay lines; and, acontroller coupled to the common contact and to each of the pixelcontrol contacts, the controller being preprogrammed to activateenergize selective ones of the pixel control contacts to change spatialdirectivity of the plurality of radiating elements.

A further aspect is a method for operating the antenna, comprising:scanning a radiation cone formed by radiating elements of the antenna;using transmissions received during the scanning, identifying specificlocations in space of each originating transmission; from theoriginating transmissions, identifying locations of unauthorizedtransmissions; controlling the antenna to present a null to directionsof the unauthorized transmissions; and performing directed communicationwith each authorized transmission by controlling the antenna to steerthe radiation cone towards the authorized directions. Scanning theradiation cone can be performed by applying voltages to change thedielectric constant presented under the delay lines of the antenna.Optionally, for each authorized transmission, identifying thetransmitting device and determining the device's network and accesspolicies, and applying the network and access policies to thecommunications from the identified device, thereby forming an “RFfirewall.”

It should be noted that in the disclosure, every reference towavelength, λ, indicates the wavelength traveling in the related medium,as the wavelength may change as it travels in the various media of theantenna according to its design and the DC potential applied to variabledielectric matter within the antenna.

FIG. 8 illustrates an omni-directional steerable antenna that can beconstructed using any of the disclosed embodiments. The antennacomprises four sides, or facets, wherein each side includes a 2×4 arrayof radiating elements 835, interconnected via delay lines 840. Thestructure of each of the facets, including the radiating elements 835,the delay lines, 840, and the feed lines may be done using any of theembodiments disclosed herein. By controlling the dielectric constantunder each of the delay line, the radiation cone of each facet can besteered in space; thus, by controlling all four facets the antenna canselectively transmit and receive selectively in any direction around theantenna. For example, the antenna can be steered to perform directionalcommunication with users A and B, but present a null towardsunauthorized user C, thus preventing user C from intruding into thesystem.

In constructing the antenna according to the disclosed embodiments, thevariable dielectric constant sandwich may be implemented by simply usingan LCD. Of course, in applications where the LCD is not visible, e.g.,WiFi access point, base station, etc., the LCD may be black and whiteonly (i.e., the color filters layer may be omitted). Also, theillumination and polarization elements of a standard LCD may bedispensed with, since they do not contribute to frequency matching orspatial scanning of the antenna array. Also, if the antenna is notvisible, the patches and feed lines may be made of solid metal, such ascopper and aluminum. When the antenna is visible, the patches and feedlines may be made of transparent conductor, such as an ITO, AZO, etc.

In this sense, one embodiment of the invention may be characterized asproviding an antenna comprising: an LCD screen having a common groundcontact, a plurality of addressable pixel contacts, and a topdielectric; an array of radiating elements provided over the topdielectric; conductive delay lines, each connected to one of theradiating elements; and a transmission feed provided below the LCDscreen and coupled to the delay lines. A controller is coupled to thecommon contact and to each of the addressable pixel contacts, thecontroller being preprogrammed to energize selective ones of the pixelcontrol contacts to change the spatial directivity of the radiatingelements.

Using software control to scan the flat antenna array, one can achievescanning in two-dimensions in space. Thus, for example, such an arraycan be used as a flat satellite TV antenna. The antenna can be placed onthe roof, such that it is not visible from street level. Since thespatial directivity of the array can be controlled electrically usingsoftware, the antenna need not be mechanically aimed at the satellite,as do conventional dish antennas. Rather, the satellite can be acquiredby scanning the antenna electrically by changing the voltages applied tothe electrode of the variable dielectric layer (i.e., changing theimages projected on the LCD screen when an LCD is used), until the bestreception is achieved.

Due to the proliferation of mobile devices, conventional access points,such as WiFi access points, are loaded with interfering transmissions.Specifically, since standard access points use omni-directionalantennas, the access point transmits and receives in all directions.Therefore, in transmission the access point must use high energy, sincethe transmitted energy drops inversely to the distance cubed for anomni-directional antenna. Moreover, the access point's transmission addsto the interference of the multiple mobile devices (smartphones, pads,laptops), each of which uses omni-directional antenna that interfereswith everyone else's device.

Using the embodiment illustrated in FIG. 8, an access point can befabricated that receives and transmits to a specific direction. That is,prior to the transmission to a particular device, the voltage of theelectrodes of the VDC plate can be changed such that the antenna isaimed at the target device. Since the transmission is at high frequency,and since the antenna can be scanned electronically, the antenna can bere-directed each time it transmits to a different mobile devicepositioned at different spatial location with respect to the accesspoint.

Moreover, as shown in FIG. 8, multiple arrays may be used, eachcontrolled individually, since each pixel on the VDC plate can becontrolled individually. Furthermore, while in FIG. 8, the fourindividual arrays are placed on four individual facets, otherarrangements can be made, e.g., three facets of a triangle, five facetsof a pentagon, etc. In this manner, each array is directed to adedicated spatial area and the arrays together cover 360 around theaccess point.

Also, the software defined antenna system described herein can provide asignificant advantage when applying policies, security schemes andaccess to wireless communication, such as WiFi access point. Forexample, since the antenna can be scanned to cover 360°, it provides theability to dynamically create a 3D map of the environment of users,interference signals and intruders. By properly operating the phasedarray scanning capability of the array, the system can identify andisolate an unauthorized user, e.g., an intruder, in space, inspect itscharacteristics, and decide to eliminate its ability to connect to thenetwork by creating a null in space that can then track and prevent thatintruder from ever reaching the network. In a sense this creates awireless fire-wall at the wave-port level. Additionally, optionally thesystem can identify each approved user (e.g., using MAC address) perlocation in space around the antenna, and determine what network andaccess policies privileges apply to the particular user. For example,different network and access policies will apply to an employee than toa visitor at a company. The system can then apply network and accesspolicies based on location in space of the Tx/Rx. Since the softwaredefined antenna is able scan and to track users by forming directionalbeams and nulls, the network and access policies can be maintained foreach identified user.

FIG. 9 illustrates a method for operating the antenna according to anembodiment utilizing any of the software defined antennas describedherein. After start, the system scans the antenna by, e.g., applyingvoltages to change the dielectric constant presented under the delaylines of the antenna. Using transmissions received during the scan, thesystem identifies specific location in space of each originatingtransmission. From the set of identified transmissions, the system thenidentifies locations of unauthorized transmissions. The system thencontrols the antenna to present a null to the unauthorized directions.The system then performs directed communication with each authorizedtransmission by controlling the antenna to form a beam directed at theauthorized direction. Optionally, as shown in broken-line, for each userthe system identifies the transmitting device and determines thedevice's network and access policies. The system then applies thenetwork and access policies to the communication from the identifieddevice.

FIG. 10 is a block diagram illustrating how the antenna of any of thedisclosed embodiments can be incorporated in a standard IEEE 802.11Naccess point. The structure and elements of the standard access pointare well known in the art and need not be explained here. In the exampleof FIG. 10, the standard antenna is replaced by a software definedantenna. Also, the microprocessor (MPU) is programmed to provide therequired voltages to steer the antenna or to change the resonancefrequency of the radiating patches.

In this sense, embodiments of the invention may be characterized asproviding a wireless access point, comprising: a transceiver; an antennaarray comprising an LCD screen having a common contact, a plurality ofpixel control contacts, and a top dielectric; an array of radiatingelements provided on top of the top dielectric; and plurality of delaylines, each connected to one of the radiating elements; a plurality offeed lines connected at one end to the transceiver and the opposite endone of the delay lines; and, a controller coupled to the common contactand to each of the pixel control contacts, the controller beingpreprogrammed to activate energize selective ones of the pixel controlcontacts to change spatial directivity of the plurality of radiatingelements.

The disclosure now turns to providing methods for fabricating an antennaaccording to the disclosed embodiments. As noted, the disclosedembodiments utilize various insulation plates or substrates, which maybe PCB material, Teflon®, glass, Rohacell® (available from EvonikIndustries AG of Essen, Germany), etc. For brevity, these substrateswill be referred to in the following description as top substrate andbottom substrate. In FIG. 11, the top substrate 1101 may be compared to,e.g., the cover insulating layer 617 of FIG. 6, while the bottomsubstrate 1103 may be compared to the back plane dielectric 612 of FIG.6.

At step 1100 of FIG. 11, the top substrate is fabricated by forming aradiating element 1135 on the top surface and delay lines 1140 on thebottom surface of the substrate 1102. Ohmic contact 1119 may connect thedelay line 1140 to the radiating element 1135. Alternatively, the delayline 1140 and the radiating element 1135 may be connected capacitivelyacross the substrate 1102. Also, in this embodiment the electrodes foractivating the liquid crystal pixels are omitted. Instead, activationline 1121 is formed on the bottom surface of the top substrate and isconnected to the delay line. The activation line is connected to abias-T to separate its signal from the RF signal.

Specifically, the callout in FIG. 11 illustrates a standard Bias-Tcircuit. The RF+DC node is coupled to the delay line 1140. The DC nodecorresponds to the output of a variable voltage potential used tocontrol the state of the liquid crystals. The RF node corresponds tofeed lines 1155 of the corporate feed. As shown in FIG. 11, the RF nodeis coupled to the circuit via capacitor C. However, as explained herein,the RF signal in the disclosed embodiments is already coupled to thedelay line capacitively, such that capacitor C may be omitted. Thus, byincorporating inductor I into the DC side of the antenna, a modifiedBias-T circuitry is created.

In step 1105 the bottom substrate 1103 is fabricated by forming theground plane 1125 on the top surface, with the appropriate apertures1123 strategically situated to allow the RF signal to be transmittedtherethrough. Also, the conductive lines 1155 of the corporate feed arefabricated on the bottom surface of the bottom substrate 1103.

At step 1110 an alignment layer 1104 is formed on the top surface of thebottom substrate 1103, the bottom surface of the top substrate 1102, orboth. The alignment layer may be formed by depositing an alignmentmaterial, such as, e.g., polyimide, and modifying the alignment materialto function as an alignment layer for the liquid crystals. Themodification may be achieved by rubbing in a desired alignmentdirection, forming scratches in the alignment directions, or UV curing.The description proceeds with the assumption that the alignment layer1104 was formed at least on the top surface of the bottom substrate1103.

At step 1115 spacers 1106 are placed on top of the alignment layer 1104,which as noted above, in this case is assumed to be the top surface ofthe bottom dielectric 1103. In this embodiment the spacers are glass orzirconia balls. In one embodiment, the balls are adhered to thealignment layer 1104 using adhesive. In one embodiment, the balls areadhered to the alignment layer 1104 using, e.g., UV curable epoxy, inwhich case after placing the spacers the bottom substrate 1103 isexposed to UV radiation to cure the adhesive and secure the spacers intheir locations.

At step 1120 a dam or seal 1107 is placed on the top surface of thebottom substrate 1103. The seal 1107 may be a bead of silicon or epoxy,a pre-formed frame of sealant material, etc. The seal encloses the areato be occupied by liquid crystal and prevent the liquid crystal fromspilling out of the sandwich forming the antenna. At step 1125 liquidcrustal 1165 is flown onto the top surface of the bottom substrate 1103.Thereafter, at step 1130, the top and bottom substrates are broughttogether to form the multilayer sandwich of the antenna. Depending onthe various adhesive and sealants used, the entire sandwich may beexposed to UV radiation for curing.

FIG. 11A illustrates a modified method, wherein the process flow issimilar to that of FIG. 11, except that rather than using an activationline connected to the delay line to activate the liquid crystal,electrodes 1620 are formed on the bottom surface of the top substrateand potential lines 1121 and ground lines 1121′ are attached to theelectrodes, to thereby define pixels.

FIG. 12 illustrates another method for fabricating the antenna. In FIG.12 steps 1200 to 1220 are the same as those of steps 1100 to 1120 ofFIG. 11. However, in FIG. 12 at step 1225 the top and bottom substratesare brought together to form the multilayer sandwich of the antenna.Then in step 1230 an injector 1170 is used to inject liquid crystal intothe void defined by the top and bottom substrates and bounded by theseal 1107. The injection can be done through an injection hole that issealed after the injection of the liquid crystal.

FIG. 13 illustrates yet another embodiment wherein different types ofspacers are used, or a spacer-sealer combination is used. In FIG. 13steps 1300 to 1310 are the same as those of steps 1100 to 1110 of FIG.11. However, in FIG. 13, in step 1315 a spacer or a spacer-sealercombination is used. In one example, a spacer 1317 is the form of a gridof dielectric material is used, such as that illustrates in the topcallout in FIG. 13. The spacer is formed separately as a grid of anydesired shape, e.g., lines, squares, honeycomb, etc., and is then placedon top of the alignment layer 1104. In one specific embodiment, holes1309 are provided on the sidewalls of the grid to allow the liquidcrystal to flow and even out the liquid crystal material among all ofthe spaces generated by the grid 1317. As shown in the top view of thesecond callout, the spacer 1317 may incorporate a seal 1307 on itsperiphery, such that attaching the spacer-seal combination on top of thealignment layer 1104 is a one step, instead of two as shown in theprevious embodiments.

In step 1325 an injector 1372 is used to inject liquid crystal onto thegrid 1317, and in step 1330 the two substrates are brought together toform the multi-layer sandwich of the antenna. Alternatively, as with theembodiment of FIG. 12, the bottom and top substrates can first beattached to each other and then the liquid crystal injected through adedicated injection hole that is later sealed.

FIG. 14 illustrates a roll-to-roll method of manufacturing the antennaaccording to the embodiments of the invention. In FIG. 14, supply roll1401 provides a continuous strip of flexible insulating material, e.g.,PET, polymer nanocomposites, Pyralux® (Available from Du Pont),ECCOSTOCK® low loss dielectrics (Available from Emerson & Cuming ofLaird PLC, London, England, etc. The insulating strip 1402 is passedthrough a first metallization station 1470, wherein radiating patchesare formed on the top surface of the insulating strip. Any of themetallization station described herein may be any metal-printing capablestation, such as, e.g., micro-transfer printing, screen printing, inkjetprinting, flexographic printing, nano-imprint lithography (NIL), etc.

The insulating strip continues to a second metallization station 1472,wherein the bottom of the insulating strip is imprinted with delaylines. Depending on the design, as indicated above, the bottom of theinsulating strip may also be imprisoned with activation lines connectedto the delay lines, or with electrodes and activation lines connected tothe electrodes. In this respect, the delay lines differ significantlyfrom the electrode in that the delay lines are in the form of meanderinglines, while the electrodes are in the form of a square or circle.

Meanwhile, supply roll 1411′ provides a continuous strip of insulatingmaterial, e.g., PET. The insulating strip 1403 is passed throughmetallization station 1474, wherein ground layer is formed on the topsurface of the insulating strip 1403. The ground layer includesapertures corresponding to each of the delay lines. The insulation strip1403 is then passed through metallization station 1406 wherein the feedlines of the corporate feed are formed on the bottom surface of theinsulating strip 1403.

As noted in the other embodiment, at least one alignment layer needs tobe formed in order to align the liquid crystals. For completeness, inFIG. 14, both insulating strips are shown as being provided withalignment layers. Specifically, deposition system 1408 provides thealignment material on the bottom surface of the top insulating strip1402 and on the top surface of the bottom insulating strip 1403. Then ascrubber 1409 performs rubbing or scratching of the surface of thealignment material so as to provide the alignment. Alternatively, UVradiation can be used to form the alignment. Thus, to show both options,FIG. 14 illustrates a scrubber 1409 operating on the alignment layer ofthe top insulating strip 1402, while a UV source 1411 operates toperform the alignment on the bottom insulating strip 1403. However, itshould be appreciated that any of these methods may be used alone or incombination.

Next, in station 1412 spacers are attached to the top surface of thebottom insulating strip 1403. The spacers are attached on top of thealignment layer. If the spacers are adhered to the bottom insulatingstrip using radiation curable adhesive, then radiation source (e.g., UVsource) 1414 is provided downstream of station 1412. In the nextstation, 1416, the liquid crystal is poured onto the top surface of thebottom insulating strip. In station 1418 both insulating strips arebrought together and cured using, e.g., UV curing. In station 1420 aknife is used to separate the individually created antennas.

Note that if the illustration of FIG. 14 is flipped over a horizontalaxis, the same process can be performed, except that the spacers and theliquid crystal material will be deposited over the bottom surface of thetop insulating strip 1402.

Various embodiments were described above, wherein each embodiment isdescribed with respect to certain features and elements. However, itshould be understood that features and elements from one embodiment maybe used in conjunction with other features and elements of otherembodiments, and the description is intended to cover suchpossibilities, albeit not all permutations are described explicitly soas to avoid clutter.

Also, the terminology used herein with respect to connected and coupledfollows the convention that connected means one part is directlyconnected to the other, while coupled means that there may beintervening elements between the two parts. Also, it should beunderstood that a DC connection is akin to a DC short, wherein oneconductor physically touches the other conductor to enable DC currentflow. However, an RF coupling does not necessarily require the twoconductors to physically touch. A valid example is two capacitor plates,wherein DC current cannot be transmitted through them, but AC and RF canbe transmitted.

It should be understood that processes and techniques described hereinare not inherently related to any particular apparatus and may beimplemented by any suitable combination of components. Further, varioustypes of general purpose devices may be used in accordance with theteachings described herein. The present invention has been described inrelation to particular examples, which are intended in all respects tobe illustrative rather than restrictive. Those skilled in the art willappreciate that many different combinations will be suitable forpracticing the present invention.

Moreover, other implementations of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. Various aspects and/orcomponents of the described embodiments may be used singly or in anycombination. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

The invention claimed is:
 1. A method for fabricating a multilayeredantenna, comprising the non-ordered steps of: fabricating a topsubstrate by forming radiating elements on a top surface of a firstinsulating plate, and forming a plurality of corresponding delay lineson a bottom surface of the insulating plate; fabricating a bottomsubstrate by forming a common ground electrode on a top surface of asecond insulating plate, the common ground electrode having a pluralityof apertures, and forming a plurality of conductive feed lines on abottom surface of the second insulating plate; forming an alignmentlayer over: the top surface of the bottom substrate, over the bottomsurface of the top substrate, or on the top surface of the bottomsubstrate and over the bottom surface of the top substrate; providinginsulating spacers over the alignment layer; attaching a sealer over theperiphery of the top surface of the bottom substrate or the bottomsurface of the top substrate; flowing liquid crystal among theinsulating spacers; and, attaching the bottom substrate to the topsubstrate.
 2. The method of claim 1, wherein providing insulatingspacers comprises placing a plurality of insulating spheres.
 3. Themethod of claim 1, wherein providing insulating spacers comprisesadhering a plurality of insulating spheres to the alignment layer. 4.The method of claim 1, wherein providing insulating spacers comprisesforming a grid made of insulating material and placing the grid over thealignment layer.
 5. The method of claim 4, further comprising formingflow holes in the grid to enable the liquid crystal to flow amongelements of the grid.
 6. The method of claim 5, wherein flowing liquidcrystal among the insulating spacers comprises injecting the liquidcrystal through a dedicated injection hole after the step of attachingthe bottom substrate to the top substrate.
 7. The method of claim 4,further comprising attaching the sealer over periphery of the grid. 8.The method of claim 1, wherein flowing liquid crystal among theinsulating spacers comprises injecting the liquid crystal after the stepof attaching the bottom substrate to the top substrate.
 9. The method ofclaim 1, wherein fabricating a top substrate further comprises forming aplurality of activation lines, each connected to one of the delay lines.10. The method of claim 1, wherein fabricating a top substrate furthercomprises forming a plurality of electrodes on the bottom surface of thetop substrate, and forming a plurality of activation lines, eachconnected to one of the electrodes.
 11. The method of claim 1, whereinthe first insulating plate comprises one of PCB material, Teflon®,glass, or Rohacell®.
 12. The method of claim 1, further comprising:providing a first roller of first dielectric strip; providing a secondroller of a second dielectric strip; fabricating the top substratecomprises passing the first dielectric strip through metallizationstation and forming the radiating elements on top surface of the firstdielectric strip and the plurality of corresponding delay lines onbottom surface of the first dielectric strip; fabricating the bottomsubstrate comprises passing the second dielectric strip throughmetallization station and forming the common ground electrode on topsurface of the second dielectric strip and the plurality of conductivefeed lines on bottom surface of the second dielectric strip.
 13. Themethod of claim 12, wherein forming a plurality of radiating patches,forming plurality of delay lines, forming a common ground, and forming aplurality of feed lines comprises one of: micro-transfer printing,screen printing, inkjet printing, flexographic printing, nano-imprintlithography (NIL).
 14. The method of claim 12, further comprisingforming a plurality of activation lines, each coupled to one of thedelay lines.
 15. The method of claim 12, further comprising forming aplurality of electrodes and a plurality of activation lines, eachactivation line coupled to one of the electrodes.
 16. The method ofclaim 12, wherein providing the plurality of spacers comprises adheringa plurality of beads onto the first or second dielectric strips.
 17. Themethod of claim 1, wherein: feed line is being configured to communicateRF radiation to one of the radiating elements; and the plurality of RFfeed lines form a corporate feed.
 18. The method of claim 17, furthercomprising forming a plurality of electrodes on the first dielectricplate, and forming a plurality of activation lines, each connected toone of the electrodes.
 19. The method of claim 17, further comprisingforming a plurality of activation lines, each connected to one of thedelay lines.
 20. The method of claim 17, wherein providing spacerscomprises providing a grid made of dielectric material.